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VII.

PRIZE ESSAY

THE AGRICULTURAL VALUE OF PHOSPHATE OF LIME.

BY JOSEPH HARRIS, ROCHESTER, NEW YORK,

[From the Transactions of the New York State Agricultural Society.]

Phosphorus, an element never found in nature in an uncombined state, but usually manufactured from bones, is semi-transparent of nearly the consistence of wax; internally of a reddish or flesh color, but coated with a white film, arising from its partial decomposition. It so strongly attracts oxygen from the air as to become slowly decomposed at a very low temperature; and hence it is usually kept under water.

When ignited, it gives off dense white fumes. This is phosphoric acid, and it is in form united with lime, iron, lead, copper, and other bases with which it is usually found. Ít enters into the composition of all plants and animals, and is found in all soils not absolutely sterile; the inorganic parts of the bones of all animals are composed principally of this acid united with lime, called phosphate of lime; and wheat, Indian coin, Timothy, and other Cereal grains contain from forty to fifty per cent. in their ashes. It will easily be seen that it is a substance of vast importance in an agricultural point of view; and when it is understood that no plant will grow on a soil destitute of it; that no soil, however fertile, contains but a comparatively small amount, and that in the bones and flesh of animals, and in the grains of wheat, Indian corn, and Timothy, it is annually exported from the soil in large quantities never to return, its real value and importance will be clearly perceived. The whole of the phosphate of lime which exists in the bones of man and animals must have been originally in the soil, and, being taken up by plants, was by them conveyed into the animal organism. Under the system of agriculture commonly adopted, phosphate of lime is continually being abstracted from the soil, and, unless an equivalent portion to that which is taken is liberated from the soil by annual decomposition, or is returned by the purchase of manure containing it, a gradual diminution of fertility must follow. Those engaged in the pursuit of agriculture cannot but derive some benefit from a knowledge of the chemical properties and agricultural uses of phosphate of lime.

As is usually the case, practice got the start of science in the use of bones as a manure, and, without knowing why, the farmer found them of great value to his soil. It is said they were first used on the natural grass dairy meadows of Cheshire, England, where, from the large amount

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annually taken from the soil in cheese and the bones and flesh of animals, the soil had become exhausted of phosphoric acid; their effect was surprisingly beneficial. They were used with profit at a cost of from $20 to $60 per acre. Few turnips were then grown; but the value of this crop being acknowledged, great efforts were made to extend its culture, the land owners in many cases compelling the tenant farmer to grow a certain number of acres. Bones were found to be the best manure that could be applied to this crop, their beneficial effect lasting for many years. I have seen a crop of turnips three times as large on a portion of a field where bones had been applied 12 years previous as on another part of the same field where none had been used, though treated similarly in every other respect. It is often said that soil dressed with bones never forgot it when turnips were sown; but this opinion is formed from the lasting effects of roughly-broken bones, as first used at the rate of one hundred bushels per acre; it was soon found that if they were finely ground, a much smaller quantity would suffice, though the benefit would not be so lasting. The reason of this is found in the fact, that plants cannot take anything from the soil but in a state of solution. Now, bones in their natural state are insoluble in water, and have first to decompose, and be incorporated with the soil, before they can nourish plants; but, if finely ground, they are easily intimately mixed with the soil, where, being attacked by its acids, they readily decompose, and are more speedily rendered in a fit state for assimilation by the plants. Twenty bushels of dust will in this way be more beneficial, apparently, than 100 bushels of merely crushed bones.

The reason why boiled bones are supposed to be better than unboiled is the same; they have absorbed considerable water, and are, in sequence, more speedily decomposed in the soil, and taken up by the plants. Common experience proved the value of bones as a manure, but science had to explain the cause of their beneficial action. This science not only did, but, having done so, discovered a plan to decompose these bones before they were applied to the soil, thus concentrating the effect into one, which would have extended over twenty years, or producing a better effect for one year, with a twentieth part of the bones.

There are several phosphoric acid and lime compounds known to chemists; but the only two that concern us at present are the neutral phosphate of lime, often called the bone earth phosphate, because it forms the chief earthly ingredient of bones, and the bi-phosphate, or, as it is called in commerce, super-phosphate, or acid phosphate of lime.

Pure neutral phosphate of lime contains, in 100 poundsPhosphoric acid..

481 Limc...

511

con

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The bi-phosphate, or acid phosphate of lime, is composed of,
Phosphoric acid...
Lime...

711 282

100

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The neutral phosphate of lime is all but insoluble in water; but the bi-phosphate is readily soluble. Now, what science has discovered is the method of cheaply converting the insoluble phosphate into the soluble bi-phosphate; and, simple as it may seem, this discovery has benefited agriculture more than all others combined.

Phosphate of lime consists of two atoms of phosphoric acid and two of lime; and bi-phosphate has three atoms of phosphoric acid combined with one of lime. Now, to convert the one into the other, we have either to add phosphoric acid, or take away lime; the latter is the only way practical in a manufactory, though the former can be done in the laboratory. Phosphoric being what chemists term a weak acid, sulphuric acid will take away its lime, setting the phosphoric acid free. If but a small quantity of acid is applied, it will unite with a portion of the lime, forming sulphate of lime, and setting free its phosphoric acid, which will unite with the remairing phosphate of lime, forming the required soluble bi-phosphate. If sufficient acid is not added to convert the whole into bi-phosphate, a portion of the neutral phosphate will remain untouched. If more than is required to convert the whole into bi-phosphate is applied, a portion of the phosphoric acid will be liberated, and remain uncombined, and by adding sufficient acid the whole may be set free, and the result of the mixture would be sulphate of lime and free phosphoric acid.

To exemplify this, let us suppose 100 pounds of the pure phosphate of lime taken; this would contain 481 pounds phosphoric acid. Now, then, if 711 of phosphoric acid make 100 of bi-phosphate of lime, 484 will make 68. Therefore, the 100 pounds of pure phosphate of lime can be converted into 68 pounds of bi-phosphate of lime, and this is accomplished by abstracting 32 pounds of lime. The quantity of pure sulphuric acid required to effect this is easily calculated.

Sulphate of lime, or plaster, is composed of, Lime.....

411 Sulphate acid....

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100 So that 32 pounds of lime would require 45 pounds sulphuric acid to convert it into sulphate of lime. Therefore, to convert 100 pounds of neutral phosphate of lime into bi-phosphate would require 45 pounds of pure sulphuric acid. If we take away the 32 pounds of lime, we should have, as the result, 68 pounds bi-phosphate, and 77 pounds of sulphate of lime.

The composition of bones varies considerably, according to the age and kind of animals—less phosphate of lime, and more gelatine, being found in an older animal; but, on an average, 100 parts of raw bones may be estimated as containingWater....

11 lbs Phosphate of lime.. Fat and gelatine.. Carbonate of lime..

4 « Alkaline chlorides and sulphates

2 66

45 66 38 "

100

It will be seen that, besides the phosphate of lime, bones contain thirty-eight per cent. of organic matter, so that, in judging of the results of experiments with fresh bones, it is necessary to take this into account, and not attribute all the benefit to the phosphate. To avoid any discrepancies of this kind, we will present the reader with a few results selected from experiments made at Rothamsted farm, Herts, England, by Mr. Lawes and Dr. Gilbert, in which calcined bones were used containing about ninety per cent. of phosphate of lime."

TABLE I.-TURNIP EXPERIMENTS.

Description of manure.

Bulk, per acre.

Leaf, per acre.

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Unmanured....
12 cwt. sulphate lime, the refuse of tartaric acid manu-

facture...
400 pounds calcined bone dust.
400 pounds calcined bone dust and muriatic acid,

equivalent to 268 pounds sulphuric acid (sp. gr.

1.71) 400 pounds ealcined bone dust and 134 pounds sul

phuric acid (sp. gr. 17)... 400 pounds calcined bone dust and 268 pounds sul

phuric acid... 400 pounds calcined bone dust, 268 pounds sulphuric

acid, and 134 pounds common salt.. 400 pounds calcined bone dust and 400 pounds sul

phuric acid..

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The most striking feature in the above selection is the great difference between the unmanured and the manured lots. It is seen that sulphate of lime or plaster increases the amount five tons per acre, though yielding a crop which, in common practice, would not be considered remunerative. But whenever phosphate of lime is used, the effect is greatly beneficial. The difference between the decomposed and undecomposed is not so striking as I should anticipate; but the fact of the bones having been burnt and in a state of minute subdivision, making them more readily soluble, would render them much more effi cacious than bone-dust as generally applied. An increase of sulphuric acid from 134 pounds to 268 pounds, with 400 pounds of bones in each case, gives an increase of 12 cwt. of bulk and 17} cwt. of leaf; but an increase from 268 to 400 pounds of sulphuric acid, with the same amount of bones in either case, is attended with a diminution of 81 cwt. of bulk, and 11 cwt. of leaf. This will indicate the amount of acid best to use, and shows, not only the necessity of having the whole phosphate decomposed, but that it is injurious to have phosphoric acid free by using an excess of sulphuric acid; but it is the former, rather than the latter, evil that farmers need be on their guard against in purchasing super-phosphate of lime. Mr. Lawes's experiments on turnips were commenced in 1843, and have been continued to the present time, during which many interesting and important facts relative to the turnip, and the position it occupies in English agriculture, have been brought to light, which it would be inconsistent with the ob. ject of the present essay to discuss; but it may be mentioned, as amongst the most important conclusions, that, if in ordinary agriculture the turnip is supplied with available phosphate of lime, no other substance need be employed of a mineral or alkaline nature; that ammonia is not essential; but that carbon, in conjunction with phosphate, will give an increased crop over the phosphate alone.

The soil on which these experiments were made is a somewhat heavy loam, unsuitable for turnips, which delight in a light, sandy loam; so that the above weights per acre may be considered as much under the amount usually obtained on soils well adapted to their growth.

The following result was obtained by Mr. Pusey in the regular course of tillage; the bulbs only are given:

Tons. No manure, per acre

1 00 Five and a quarter bushels super-phosphate of lime, per acre.. 16 12

Cwt.

Great as this increase may appear, yet I think it may be taken as a correct estimate of the benefit usually derived from the application of super-phosphate of lime to the turnip crop. But it is as a manure for wheat that we should naturally look for the greatest benefit from superphosphate, inasmuch as this grain contains such a large amount of phosphoric acid. Mr. Lawes's experiments on wheat, on a soil similar to the one on which the turnip-experiments were made, and which had been agriculturally exhausted by the growth and removal of four grain. crops, without any manure previous to the commencement of the experiments, are very conclusive on this point. That the first year gave the following result, which may be taken as an indication of the results of after-experiments: An acre, unmanured, gave 16% bushels, and 1,120 pounds straw; with 700 pounds super-phosphate of lime, manu. factured from calcined bone dust, 16% bushels and 1,116 pounds of straw.

The following experiments, in the same year, (1844,) and on the same field, prove that the failure of the super-phosphate was not owing to a deficiency of other mineral manures or ash constituents:

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